Vaccinia virus (VACV) affords long-lasting protection against variola virus, the agent of smallpox. VACV- specific CD8 memory T cells contribute to protection but their molecular control is not fully understood. The goal of the current project is to identify and understand the role of 4-1BB, a member of the TNF receptor family, in controlling the generation and persistence of endogenous VACV-specific memory CD8 T cells, and to investigate whether targeting this molecule can enhance the efficacy of peptide or attenuated virus immunization to protect against subsequent infection. VACV is being used as a vector for vaccination against a wide range of infectious pathogens and knowledge gained from our studies will hopefully aid the development of safe but effective vaccines comprising VACV vectors. Wild type, attenuated, and recombinant vaccinia virus, containing a defined CD8 T cell epitope of ovalbumin (OVA), will be used in experiments with knockout animals lacking 4-1BB or 4-1BBL to show their contribution in generating VACV-specific CD8 T cells. Additionally, TCR transgenic CD8 T cells, reactive with VACV-OVA, and deficient in 4-1BB, will be used to specifically define the role of 4-1BB on a T cell by tracking adoptively transferred T cells in vivo. Agonist reagents to 4-1BB, alone or in combination with various other adjuvants, will be studied in terms of eliciting protective T cell populations that can neutralize lethal infections. This research should provide invaluable data on the importance of 4-1BB in controlling T cell responses to VACV and highlight its potential role as a target for future vaccination strategies. PUBLIC HEALTH RELEVANCE: Vaccinia virus (VACV) affords long-lasting protection against variola virus, the agent of smallpox. This research aims to understand the molecular control of virus-specific CD8 memory T cells that contribute to protection. This study will benefit the development of better VACV vaccines for infectious diseases as well as cancer immunotherapy.